U.S. patent application number 12/703440 was filed with the patent office on 2010-06-24 for multi-carrier incremental redundancy for packet based wireless communications.
This patent application is currently assigned to QUALCOMM Incorporated. Invention is credited to Lorenzo Casaccia, Durga Prasad Malladi.
Application Number | 20100157791 12/703440 |
Document ID | / |
Family ID | 36143135 |
Filed Date | 2010-06-24 |
United States Patent
Application |
20100157791 |
Kind Code |
A1 |
Casaccia; Lorenzo ; et
al. |
June 24, 2010 |
Multi-Carrier Incremental Redundancy For Packet Based Wireless
Communications
Abstract
Methods and apparatus are disclosed herein for providing
incremental redundancy in a wireless communication system to aid in
error recovery. One or more redundancy versions are sent on
different carriers than the primary version of information to be
transmitted. At the receiver end the redundancy versions may be
combined using hard or soft combining techniques, including
selection combining, selective soft combining or soft
combining.
Inventors: |
Casaccia; Lorenzo; (San
Diego, CA) ; Malladi; Durga Prasad; (San Diego,
CA) |
Correspondence
Address: |
QUALCOMM INCORPORATED
5775 MOREHOUSE DR.
SAN DIEGO
CA
92121
US
|
Assignee: |
QUALCOMM Incorporated
San Diego
CA
|
Family ID: |
36143135 |
Appl. No.: |
12/703440 |
Filed: |
February 10, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11238791 |
Sep 28, 2005 |
|
|
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12703440 |
|
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|
|
60615254 |
Oct 1, 2004 |
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Current U.S.
Class: |
370/216 ;
714/746 |
Current CPC
Class: |
H04L 1/1845 20130101;
H04L 5/06 20130101; H04L 1/08 20130101; H04L 1/0045 20130101; H04L
5/0055 20130101; H04L 5/0053 20130101; H04L 1/04 20130101; H04L
27/18 20130101; H04L 1/1893 20130101; H04L 1/1819 20130101 |
Class at
Publication: |
370/216 ;
714/746 |
International
Class: |
H04J 1/16 20060101
H04J001/16 |
Claims
1. A method of providing redundancy for error recovery in
multi-carrier wireless communications, the method comprising:
receiving a primary version of information encoded with a first
encoding scheme, the primary version being received on a first
carrier; and receiving a redundancy version of the information
encoded with a second encoding scheme, at least part of the
redundancy version being received on a second carrier; decoding the
primary version of the information received with the first encoding
scheme; decoding the redundancy version of the information received
with the second encoding scheme; wherein the redundancy version is
received after receiving the primary version begins and before
receiving a next said primary version, wherein said encoding
schemes provide redundancy for error recovery.
2. The method of claim 1, wherein the redundancy version is a first
redundancy version, the method further comprising: receiving, on a
third carrier, a second redundancy version of the information
encoded with a third encoding scheme; and decoding the second
redundancy version of the information with the third encoding
scheme.
3. The method according to claim 2, further comprising selectively
combining one said redundancy version, wherein one said redundancy
version is selected for use.
4. The method according to claim 2, further comprising soft
combining said redundancy versions, wherein all said redundancy
versions are combined.
5. The method according to claim 2, further comprising selectively
soft combining said redundancy versions, wherein at least one said
redundancy version is combined and at least one other said
redundancy version is discarded.
6. An apparatus for providing redundancy for error recovery in
multi-carrier wireless communications, the apparatus comprising:
means for receiving a primary version of information encoded with a
first encoding scheme, the primary version being received on a
first carrier; and means for receiving a redundancy version of the
information encoded with a second encoding scheme, at least part of
the redundancy version being received on a second carrier; means
for decoding the primary version of the information received with
the first encoding scheme; means for decoding the redundancy
version of the information received with the second encoding
scheme; wherein the redundancy version is received after receiving
the primary version begins and before receiving a next said primary
version, wherein said encoding schemes provide redundancy for error
recovery.
7. The apparatus of claim 6, wherein the redundancy version is a
first redundancy version, the apparatus further comprising: means
for receiving, on a third carrier, a second redundancy version of
the information encoded with a third encoding scheme; and means for
decoding the second redundancy version of the information with the
third encoding scheme.
8. The apparatus according to claim 7, further comprising means for
selectively combining one said redundancy version, wherein one said
redundancy version is selected for use.
9. The apparatus according to claim 7, further comprising means for
soft combining said redundancy versions, wherein all said
redundancy versions are combined.
10. The method according to claim 7, further comprising means for
selectively soft combining said redundancy versions, wherein at
least one said redundancy version is combined and at least one
other said redundancy version is discarded.
11. A communication device for providing redundancy for error
recovery in multi-carrier wireless communications, the device
comprising: a receiver for receiving a primary version of the
information encoded with a first encoding scheme, the primary
version being received on a first carrier, and receiving a
redundancy version of the information encoded with a second
encoding scheme, at least part of the redundancy version being
received on a second carrier; and a decoder for decoding the
primary version of information received with the first encoding
scheme, and decoding the redundancy version of the information
received with the second encoding scheme, wherein the redundancy
version is received after the reception of the primary version
begins and before receiving a next said primary version, wherein
said encoding schemes provide redundancy for error recovery.
12. The communication device of claim 11, wherein the redundancy
version is a first redundancy version, and wherein the receiver
receives on a third carrier, a second redundancy version of the
information encoded with a third encoding scheme and wherein the
decoder decodes the second redundancy version of the information
with the third encoding scheme.
13. The communication device according to claim 12, wherein said
decoder selectively combines one said redundancy version, wherein
one said redundancy version is selected for use.
14. The communication device according to claim 12, wherein said
decoder soft combines said redundancy versions, wherein all said
redundancy versions are combined.
15. The communication device according to claim 12, wherein said
decoder selectively soft combines said redundancy versions, wherein
at least one said redundancy version is combined and at least one
other said redundancy version is discarded.
16. A computer program product for error recovery in multi-carrier
wireless communications, comprising: computer readable medium
comprising code for causing a computer to receive a primary version
of information encoded with a first encoding scheme, the primary
version being received on a first carrier; and code for causing a
computer to receive a redundancy version of the information encoded
with a second encoding scheme, at least part of the redundancy
version being received on a second carrier; code for causing a
computer to decode the primary version of the information received
with the first encoding scheme; code for causing a computer to
decode the redundancy version of the information received with the
second encoding scheme; wherein the redundancy version is received
after receiving the primary version begins and before receiving a
next said primary version, wherein said encoding schemes provide
redundancy for error recovery.
17. The computer program product of claim 16, wherein the
redundancy version is a first redundancy version, the computer
program product further comprising: code for causing a computer to
receive, on a third carrier, a second redundancy version of the
information encoded with a third encoding scheme; and code for
causing a computer to decode the second redundancy version of the
information with the third encoding scheme.
18. The computer program product according to claim 17, further
comprising code for causing a compute to selectively combine one
said redundancy version, wherein one said redundancy version is
selected for use.
19. The computer program product according to claim 17, further
comprising code for causing a computer to soft combine said
redundancy versions, wherein all said redundancy versions are
combined.
20. The computer program product according to claim 17, further
comprising code for causing a computer to selectively soft combine
said redundancy versions, wherein at least one said redundancy
version is combined and at least one other said redundancy version
is discarded.
Description
CLAIM OF PRIORITY UNDER 35 U.S.C. .sctn.120
[0001] This application for patent is a Divisional application of
application Ser. No. 11/238,791 filed entitled Sep. 28, 2005,
entitled "Multi-Carrier Incremental Redundancy for Packet-Based
Wireless Communications," which claims priority to U.S. Provisional
Application No. 60/615,254 filed Oct. 1, 2004, entitled
"Multi-Carrier Incremental Redundancy for GERAN," and assigned to
the assignee hereof and hereby expressly incorporated by reference
herein.
BACKGROUND
[0002] 1. Field
[0003] The present invention generally pertains to the field of
wireless communications, and more particularly to the field of
error recovery in wireless communication systems.
[0004] 2. Background
[0005] Over the past two decades, cellular telephones have become
increasingly commonplace. During this same period, a number of
advances in wireless technology have afforded cellular telephones
with more features, better reception, higher bandwidth and
increased system capacity. Today's digital and packet-based
wireless systems are considerably more advanced than the first
digital wireless systems, and show great promise for the future.
GSM (Global System for Mobile Communications) was among the first
widespread digital wireless systems. GSM was introduced as a second
generation (2G) wireless system throughout Europe in the early
1990s and is now operational in over 100 countries worldwide. Over
the years the developers of GSM introduced a number of enhancements
and improvements, building on the basic voice services of GSM to
add various data and speech capabilities to the system. With these
improvements GSM has evolved into a system capable of offering a
number of enhanced digital mobile voice and data telephony services
such as Internet access, multimedia and video.
[0006] The GSM enhancements include GPRS, EDGE and GERAN. GPRS, the
General Packet Radio Service first introduced in the mid 1990s, is
a TDMA wireless packet-based network architecture based on GSM.
GPRS is based on the GSM air interface (i.e., the interface between
the terminal and the base station) and on the GSM air interface
structure of timeslots and TDMA frames. GPRS offers increased
bandwidth to users, and more efficient use of bandwidth for
operators in as much slots as may be dynamically allocated between
voice and data depending upon the demand conditions. This allows a
GPRS link to use from one to eight of the slots available per GSM
frame, at up to 22.8 kb/s for each time slot. Further, the number
of slots for the GPRS up-link and down-link may be allocated
independent of each other. GPRS employs four different coding
schemes, CS1 through CS4, each of which is a phase modulation
coding scheme using Gaussian minimal shift keying (GMSK)
modulation. GPRS supports X.25, the low speed packet transmission
protocol popular in Europe. GPRS was implemented as a step towards
implementing the EDGE system (Enhanced Data for GSM Evolution).
EDGE is an enhancement to GPRS which uses the same spectrum
allocations as existing GSM systems (e.g. GSM900, GSM1800 and
GSM1900). EDGE features nine coding schemes, four employing GMSK
modulation and five employing Eight Phase Shift Keying (8PSK)
modulation. The four EDGE GMSK coding schemes, MCS1 through MCS4,
are akin to the four GPRS coding schemes (i.e., CS1 through CS4).
The other five EDGE coding schemes, MCS5 through MCS9, use 8PSK
modulation, producing a three-bit word for every change in carrier
phase. The use of 8PSK modulation roughly triples the GPRS peak
data rates. Another enhancement to GSM, GERAN (GSM Edge Radio
Access Network) supports the EDGE network as an alternative radio
access network compatible with the 3G GSM-evolved Core Network
(CN). The GERAN architecture allows connection to the A, Gb and Iu
interfaces of the CN. GERAN is being implemented to deliver
packet-based real time wireless services including speech,
multimedia, video and Internet access.
[0007] Despite the improvements in coding schemes and enhanced
features, from time to time, errors occur in wireless systems due
to poor reception conditions. To recover from reception errors,
EDGE, and the enhancements and services associated with it, provide
an incremental redundancy error recovery scheme. When a
transmission fails due to the detection of an error, the mobile
receiver sends an automatic repeat request (ARQ) back to the base
station. In response to the ARQ, the base station transmits the
failed transmission using a different encoding scheme. Error
recovery is performed by combining the initial message with the
second version of the message retransmitted using a different
encoding scheme. This conventional system of error recovery
increases the likelihood of recovering a failed message, but
results in delays due to the ARQ being sent back to the source of
the message with a request to retransmit another version encoded
differently.
SUMMARY
[0008] In one embodiment, a method of providing redundancy for
error recovery in multi-carrier wireless communications is
provided. The method comprises encoding a primary version of
information to be transmitted with a first encoding scheme and
encoding a redundancy version of the information to be transmitted
with a second encoding scheme. The method further comprises
transmitting the primary version of the information encoded with
the first encoding scheme, the primary version being transmitted on
a first carrier, and transmitting the redundancy version of the
information encoded with the second encoding scheme, at least part
of the redundancy version being transmitted on a second carrier.
The redundancy version is transmitted in response to transmitting
the primary version of the information within a same transmission
time period as the primary version.
[0009] In another embodiment, a communication device for providing
redundancy for error recovery in multi-carrier wireless
communications is provided. The device comprises an encoder for
encoding a primary version of information to be transmitted with a
first encoding scheme, and encoding a redundancy version of the
information to be transmitted with a second encoding scheme. The
device further comprises a transmitter for transmitting the primary
version of the information encoded with the first encoding scheme,
the primary version being transmitted on a first carrier, and
transmitting the redundancy version of the information encoded with
the second encoding scheme, at least part of the redundancy version
being transmitted on a second carrier. The redundancy version is
transmitted in response to transmitting the primary version of the
information within a same transmission time period as the primary
version.
[0010] In another embodiment, an apparatus for providing redundancy
for error recovery in multi-carrier wireless communications is
provided. The apparatus comprises means for encoding a primary
version of information to be transmitted with a first encoding
scheme and means for encoding a redundancy version of the
information to be transmitted with a second encoding scheme. The
apparatus further comprises means for transmitting the primary
version of the information encoded with the first encoding scheme,
the primary version being transmitted on a first carrier, and means
for transmitting the redundancy version of the information encoded
with the second encoding scheme, at least part of the redundancy
version being transmitted on a second carrier. The redundancy
version is transmitted in response to transmitting the primary
version of the information within a same transmission time period
as the primary version.
[0011] In another embodiment, a computer readable media embodying a
method for error recovery in multi-carrier wireless communications
is provided. The method comprises encoding a primary version of
information to be transmitted with a first encoding scheme and
encoding a redundancy version of the information to be transmitted
with a second encoding scheme. The method further comprises
transmitting the primary version of the information encoded with
the first encoding scheme, the primary version being transmitted on
a first carrier, and transmitting the redundancy version of the
information encoded with the second encoding scheme, at least part
of the redundancy version being transmitted on a second carrier.
The redundancy version is transmitted in response to transmitting
the primary version of the information within a same transmission
time period as the primary version.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The accompanying drawings, which are incorporated in and
constitute part of the specification, illustrate various
embodiments of the invention, and, together with the general
description, serve to explain the principles of the foregoing
embodiments.
[0013] FIG. 1A depicts a wireless network architecture that
supports mobile stations and client devices in accordance with at
least one embodiment;
[0014] FIG. 1B depicts details of a base station and a wireless
mobile unit in a wireless network;
[0015] FIG. 2A depicts an RLC/MAC block of information being
allocated into a GSM structure of timeslots and frames;
[0016] FIG. 2B illustrates an exemplary incremental redundancy
scheme;
[0017] FIG. 3 depicts a radio block being transmitted via a
multi-carrier transmission system in accordance with at least one
embodiment;
[0018] FIG. 4 is a multi-carrier system implementing an incremental
redundancy scheme in accordance with at least one embodiment;
[0019] FIG. 5 depicts incremental redundancy in accordance with at
least one embodiment in EDGE with variable time-frequency
spreading;
[0020] FIG. 6 depicts a multi-carrier, multi-redundancy in
accordance with at least one embodiment which provides redundancy
for error recovery purposes;
[0021] FIG. 7 depicts a method of setting up the initial parameters
for practicing at least one embodiment;
[0022] FIG. 8 depicts a method to provide error recovery for
wireless communication systems in accordance with at least one
embodiment; and
[0023] FIG. 9 depicts a block diagram of a method of decoding and
combining redundancy versions according to at least one
embodiment.
DETAILED DESCRIPTION
[0024] FIG. 1A depicts a typical wireless network architecture that
supports mobile stations and client devices in accordance with
various embodiments. FIG. 1A is a block diagram which illustrates
components of a typical wireless network 110, and its interrelation
with the elements of an exemplary embodiment. Downstream from the
network 130 a wireless system typically has three broad categories
of components: the core network controllers (SGSN 102), the base
stations (BSC/BTS 104) and wireless mobile units 120. Although the
network controller in the figure is labeled as a Serving GPRS
Support Node (SGSN) 102, in some implementations it may take other
forms or be called other names, for example, a mobile switching
center (MSC). Generally, an SGSN is the core network entity dealing
with packet-switched connections, while the MSC is the core network
entity dealing with circuit-switched connections. Similarly, the
figure depicts base station controllers/base transceiver station
(BSC/BTS) 104 which may sometimes take other forms or be referred
to by other names, for example base station system (BSS). Mobile
units 120 are known by many different names, for example, cellular
telephones, mobile stations, wireless handsets, pocket bells, etc.
The scope of the invention covers these other terms, e.g., MSC,
BSS, and the like.
[0025] The wireless network shown is merely exemplary and may
include any system that allows communication with mobile wireless
devices, such as mobile units 120 that communicate over-the-air
between and among each other and/or between and among components
connected via a wireless network 110. Such mobile units 120 include
without limitation one or more cellular telephone 112, PDA
(personal digital assistant) 114, pager 116, navigation device 118,
wirelessly connected computer 128, music or video content download
unit 122, wireless gaming device 124, inventory unit 126, or other
like types of wireless devices. Cellular or other wireless
telecommunication services may communicate with a carrier network
through a data link or other network link via the fixed network 130
which may be the PSTN (public switched telephone network), ISDN,
the Internet, a LAN, WAN, or other such network. Signaling between
SGSN 102 and the fixed network 130 may be performed using Signaling
System Number 7 (SS7) protocol. SS7 is used for trunk signaling in
ISDN and widely used in current public networks.
[0026] The wireless network 110 controls messages or other
information, typically sent as data packets, sent to a SGSN 102.
Each SGSN 102 is generally connected to one or more BSC/BTS 104.
The SGSN 102 acts within the wireless network 110 in a manner akin
to a normal switching node of a landline network (e.g., PSTN or
ISDN). SGSN 102 includes the logic, for example in a processor 106,
to manage and control the mobile units 120. The processor 106 or
other logic manages and controls functions such as call routing,
registration, authentication, location updating, handovers and/or
encoding schemes for the mobile units 120 registered at the BSC/BTS
104 base stations associated with the SGSN 102. Another piece of a
typical wireless network is the Operations and Maintenance Center
(OMC), which may be considered part of the processor 106 or other
logic. The OMC organizes the operation and setup of the wireless
network.
[0027] In a similar manner to the network 130, the SGSN 102 is
connected to a number of BSC/BTS 104 by a network configured for
data transfer and/or voice information. In this way, within the
wireless network 110, communications to and from various SGSNs 102
and BSC/BTSs 104 typically use a network of landlines, the Internet
and/or a public switched telephone network (PSTN). The base station
subsystem, including BSC/BTS 104, controls the radio link with the
mobile units 120. Within the base station subsystem, BSC/BTS 104
has one or more transmitters and receivers to send and receive
information to/from mobile units 120. BSC/BTS 104 broadcasts data
messages or other information wirelessly to the mobile units 120,
such as cellular telephone 112, by over-the-air (OTA) methods. The
BSC/BTS 104 communicates with mobile units 120 across the Um
interface, also known as the air interface or radio link. FIG. 1B
depicts details of a BSC/BTS 104 and a wireless mobile 120. Each
base station BSC/BTS 104 includes an encoder/decoder 105 which
encodes/decodes information in the protocol or encoding scheme for
transmission/reception. The base station BSC/BTS 104 also includes
a processor 101 capable of performing or controlling routines and
processes involved in wireless communications, and may also be
configured to include a memory 103 for storing the various
protocols, routines, processes or software to be used in conducting
wireless communications. For example, the memory 103 may store one
or more transmission strategies for communicating with various
mobile units 120. The transmission strategies include information
concerning the number of redundancy versions to be sent, the timing
for transmitting the redundancy version (or versions) relative to
the primary version, and any encoding schemes or protocols to be
used for the transmission and reception of wireless communications.
This information may also be stored in a memory 108 of the SGSN
102, and communicated to the base station BSC/BTS 104 as needed.
Embodiments of the mobile units 120, as can be seen in the detail
of cellular telephone 112 shown in FIG. 1B, may be configured to
include a processor 107, memory 109 and encoder/decoder 111 which
perform functions similar to the corresponding parts of the BSC/BTS
104. Mobile units 120 may also have an antenna 113, a receiver
section 115 and other electronics known to those of ordinary skill
in the art for wirelessly receiving information which may entail
monitoring for, and receiving, transmissions sent simultaneously or
overlapping on different carriers in a multi-carrier wireless
system.
[0028] The wireless network 110 includes at least one Home Location
Register (HLR) and a number of Visitor Location Registers (VLRs)
(not shown) which provide information for call-routing and roaming.
The HLR, typically centralized within wireless network 110,
contains the administrative information for each mobile unit 120
registered in the wireless network 110, along with the current
location of the mobile unit 120. The HLR could be implemented as a
distributed database, although there is logically only one HLR per
network. Each SGSN 102 of the wireless network 110 has associated
with it a Visitor Location Register (VLR) stored in the memory 108
of the SGSN/MSC 102. The VLR stores selected administrative
information from the centralized HLR for use in call control and
the provisioning of the subscriber services for each mobile unit
120 currently under control of the SGSN/MSC 102. There are
generally two other registers used for authentication and security
in a wireless network 110, an Equipment Identity Register (EIR) and
an Authentication Center (AuC). The EIR is a database of all valid
mobile units 120 associated with the network. The mobile units 120
are identified within the EIR by their unique International Mobile
Equipment Identity (IMEI). The AuC contains copies of the secret
key stored in each mobile unit 120 for use in authentication and
encryption over the radio channel. It should be noted that the
SGSN/MSC 102 itself does not contain the information about
particular mobile units 120. The mobile unit 120 information is
typically stored within the HLR and VLRs.
[0029] Mobile units 120 are generally equipped with a Subscriber
Identity Module (SIM), a smart card that identifies the mobile unit
120 enabling it to make and receive calls at that terminal and
receive other subscribed services. The IMEI of the wireless unit
120 stored on the SIM card uniquely identifies that particular
mobile unit 120. The SIM card also has stored on it an
International Mobile Subscriber Identity (IMSI) used to identify
the subscriber to the system, along with a copy of the secret key
from the AuC register for authentication, and other information
pertaining to security, identification and communication protocols.
Each mobile unit 120 has installed on it, or otherwise downloads,
one or more software applications, such as games, news, stock
monitors, and the like. The mobile unit 120 includes logic which
may be configured in the form of one or more processing circuits
executing resident configured logic, microprocessors, digital
signal processors (DSPs), microcontrollers, or other like
combination of hardware, software and/or firmware containing
processors and logic configured to at least perform the operations
described herein.
[0030] The wireless communication between each of the mobile units
120 and the BSC/BTS 104 may be based on any of several different
technologies, such as CDMA (code division multiple access), TDMA,
FDMA (frequency division multiplexed access), OFDM (orthogonal
frequency division multiplexing) and any systems using a hybrid of
coding technologies such as GSM, or other like wireless protocols
used in communications or data networks, so long as the system or
protocol provides simultaneous multi-channel (e.g., multi-carrier)
communications. A carrier may be thought of as a particular
frequency (or frequency band) at a given point in time. The concept
of a channel encompasses a carrier, but may be more broadly thought
of to include spatial diversity (e.g., different communication
links) or other like type of communication paths which may be
simultaneously received by a receiver. Data communication typically
takes place between the mobile unit 120, BSC/BTS 104 and SGSN 102.
The SGSN 102 may be connected to multiple data networks such as a
carrier network, PSTN, the Internet, a virtual private network, and
the like, thus allowing the client device access to a broader
communication network. As discussed in the foregoing, in addition
to voice transmission, data may be transmitted to the client device
via SMS or other OTA methods known in the art.
[0031] FIG. 2A depicts an RLC/MAC block of information being
allocated into a structure of timeslots and frames. GSM is used
herein as an exemplary system to explain the RLC/MAC concepts and
frame structure. Embodiments of the invention may be incorporated
in other wireless systems as well. GSM allocates its available
radio spectrum using such a scheme which combines aspects of TDMA
(Time Division Multiple Access) and FDMA (Frequency Division
Multiple Access). GSM uses FDMA concepts to divide its available
bandwidth carrier frequencies spaced 200 kHz apart. Typically, each
base station has several of these carrier frequencies assigned to
it. Time division, a TDMA concept, is achieved in GSM by having
each of the carrier frequencies divided into timeslots 205 as shown
in FIG. 2A. GSM timeslots last 15/26 ms (0.577 ms). The terms
"timeslots" and "burst periods" may be used interchangeably. There
are eight 0.577 ms timeslots 205 in each GSM TDMA frame 207 lasting
4.615 ms. A GSM physical channel may be thought of as one timeslot
205 per TDMA frame 207. For example, a physical channel could
consist of the timeslot "0" (205) in each of the sequence of TDMA
frames "x" through "x+3" (207) shown in FIG. 2A. A wireless link on
a channel may occupy the same timeslot 205 (e.g., timeslot 0)
within each of a series of TDMA frames 207, for the duration of the
link or at least until a new channel is assigned. Channels may
either be dedicated channels allocated to a particular mobile
station for a call, or may be common channels used by a number of
mobile stations in idle mode on an as-needed basis.
[0032] In the GSM system, the framing scheme may be set up in
different ways according to the function being carried out. One
such channel is full rate GSM traffic channels (TCH). TCH carry
speech and data traffic and may be grouped in multiframes
consisting of 26 frames. That is, each TCH multiframe includes 26
TDMA frames. (Multiframes may be defined to contain different
numbers of frames aside from 26 frames; e.g., 52 frame
multiframes.) Each 26-frame multiframe is 120 ms long (120
ms/26=4.615 ms=one frame). Hence, one multiframe (120 ms) divided
by 26 frames divided by eight burst periods per frame, is equal to
one burst period (timeslot) of approximately 0.577 ms. The 26
frames in a GSM multiframe include 24 traffic frames, one frame
dedicated to the Slow Associated Control Channel (SACCH), and
another frame which, at the present time, remains undefined and is
not used. In order to afford some time between when a mobile
station is transmitting and when it is receiving, uplink TCHs and
downlink TCHs are separated in time by three burst periods. In
addition to full-rate TCHs (TCH/F), there are half-rate TCHs
(TCH/H). There are also eighth rate TCHs, sometimes called
Stand-alone Dedicated Control Channels (SDCCH), which are used
mainly for transmitting location updating information. The use of
half-rate TCHs effectively doubles the system capacity as compared
to communications using full-rate THCs since TCH/H speech coding is
performed at 7 kbps rather than 13 kbps for full rate TCH/F.
[0033] FIG. 2A shows an RLC/MAC 201 block mapped onto one radio
block 203 and then onto four timeslots 205 belonging to four
sequential TDMA frames 207 of a GSM multiframe. The Layer 2
transmission protocol of GPRS/EDGE is RLC/MAC. RLC (Radio Link
Control) is a sublayer of the radio interface that provides
reliability, and MAC (Medium Access Control) is the lower of the
two sublayers of the Data Link Layer and handles access to a shared
medium. RLC/MAC provides the control and coordination necessary for
GPRS wireless communications. In GPRS, one RLC/MAC 201 block is
transmitted as part of one radio block 203. The radio block 203 is
sent via four consecutive GPRS timeslots 205, which are transmitted
on a GPRS timeslot multiframe, for example, a 24 timeslot
multiframe as described above or possibly a 52 timeslot multiframe.
The inter-timeslot distance between each of the four timeslots 205
containing the radio block is eight timeslots, or the length of one
TDMA frame 207. The content of the four timeslots 205 is simply the
sequence of the four portions of the RLC/MAC 201 block itself.
Since GPRS does not provide any incremental redundancy for error
recovery, there is no incremental redundancy relationship among the
four timeslots 205, and they do not contain any redundant
information of the radio block data 203. However, an incremental
redundancy scheme is provided in EDGE in which redundancy versions
are sent at different points in time on the same carrier.
[0034] FIG. 2B illustrates an exemplary incremental redundancy
scheme. Incremental Redundancy may be employed in EDGE within the
RLC/MAC protocol, at Layer 2. If no errors are detected in an
RLC/MAC block that is sent to a mobile station, the RLC/MAC block
is passed to the next layer for processing. For example, if no
errors had been detected in the first transmission 211 of FIG. 2B
(an RLC/MAC block encoded with MCS-6) it would have been passed to
the next layer with no retransmissions, and retransmission blocks
213 and 215 would not have been sent. In the present EDGE
implementation, for a negatively acknowledged RLC/MAC block in
which an error is detected the mobile sends an automatic repeat
request (ARQ) back to the base station. In response to the ARQ, the
base station retransmits the RLC/MAC block using a different MCS
(Modulation and Coding Scheme). The retransmitted block(s) are
typically recombined with the first block, thus enhancing the
redundancy and increasing the chances of recovering the RLC/MAC
block free of errors. This situation is depicted in FIG. 2B
assuming an error was detected in the first transmission block 211
resulting in an ARQ being sent back to the base station. In
response to the ARQ the same information was sent again in
retransmission blocks 213 and 215, this time encoded in MCS-3.
Since a different modulation and coding scheme was used for the
retransmission (MCS-3) versus the first transmission (MCS-6), it
took two retransmission blocks instead of one to communicate the
data. The retransmission, in this example, used the first
retransmission part 213 and the second retransmission part 215 to
communicate the data.
[0035] Most embodiments of the invention encode the redundancy
versions using a different encoding scheme (e.g., a different MCS)
than that of the primary version. This provides incremental
redundancy rather than merely providing redundancy by sending
redundant versions encoded in the same scheme. However, some
embodiments of the invention may encode the redundancy version
using the same MCS if it is likely that errors arose due to
reception conditions associated with a particular carrier.
Conventional implementations of EDGE do not retransmit a negatively
acknowledged RLC/MAC block using the same MCS as the original
transmission because errors caused by prevailing adverse conditions
of the air interface would most likely produce a similar result
containing errors since conventional implementations of EDGE send
redundancy versions using the same carrier as the primary
version.
[0036] When a different MCS is employed for redundancy versions,
there are some constraints regarding the choice of encoding
schemes. MCS coding schemes are categorized within families (e.g.,
family A, B or C). If a different MCS is used for a redundancy
version, it should be chosen from the same "family" of the MCS used
in the first transmission. For example, FIG. 2B depicts a
negatively acknowledged MCS-6 RLC/MAC block 211 being retransmitted
using two MCS-3 blocks 213 and 215. This is appropriate since MCS-6
and MCS-3 both belong to Family A. Additionally, when a lower MCS
is used, the retransmitted RLC/MAC blocks may need more radio
blocks than the first transmission since the same information is to
be retransmitted with a lower code rate. This is depicted in FIG.
2B, which shows that the first transmission 211 being sent with
MCS-6 in one radio block needs two radio blocks 213 and 215 due to
the retransmission being performed with MCS-3.
[0037] As shown in FIG. 2B, the interval between the first MCS-6
transmission 211 and the first MCS-3 transmission 213 is larger
than the interval between the two MCS-3 transmissions 213 and 215.
In a conventional incremental redundancy implementation for EDGE,
which sends the redundancy versions on the same carrier, this time
interval before transmission of the redundancy version is due to
the negative acknowledgement process in EDGE; e.g., an ARQ being
sent back to the base station. The negative acknowledgement process
in EDGE is RLC-based and therefore relatively time-consuming.
Following the failure of the first transmission 211 in a
conventional EDGE incremental redundancy implementation, an
acknowledgement signal (not shown) needs to be sent back to the
sender before beginning the retransmissions. The duration of this
interval is implementation-dependent and is based on the RLC/MAC
settings. Embodiments of the invention are not limited in this way,
since there is not necessarily a requirement for an ARQ. Instead,
the redundancy versions are transmitted as part of a predefined
scheme (e.g., in response to the primary version be transmitted,
encoded or otherwise processed) rather than being sent in response
to the ARQ. In some embodiments, the redundancy version may be sent
according to a predefined transmission strategy within the same
transmission time period as the primary version, but not
necessarily at the same time. For the purposes of timing the
transmissions of primary and redundancy versions, a transmission
time period is defined herein as any time after the transmission of
the primary version begins up until the start of the next primary
version, assuming the next primary version is not delayed due to a
reception error. In other embodiments, the transmission time period
may be defined as a predefined value that is less than the time it
takes an ARQ signal to be received back at the transmitter
following a reception error. A transmission strategy is defined as
a predefined plan for the number of redundancy versions to be sent,
the timing for sending the redundancy version(s) relative to the
primary version, and the encoding schemes to be used for the
primary version and the one or more redundancy versions. While some
embodiments send redundancy versions following the primary version
but within the same transmission time period as the primary
version, other embodiments send the redundancy versions
simultaneous to the primary version, as discussed in conjunction
with FIGS. 3-4 and 6.
[0038] FIG. 3 depicts a radio block 303 being transmitted via a
multi-carrier transmission system in accordance with the invention.
This figure is typical of embodiments of the present invention
which include enhanced incremental redundancy error recovery for
GERAN or other wireless systems based on a multi-carrier
architecture and on the introduction of OFDM (orthogonal frequency
division multiplexing). A number of multi-carrier wireless
transmission systems exist which may be used with the invention,
including various formats of multi-carrier CDMA, spread spectrum
communications systems, or OFDM. Other such communication systems
may be used so long as they are characterized by the use of
simultaneous multiple channels; e.g., multi-carrier systems such as
Multi-Carrier GPRS (MC-GPRS). The invention allows such
multi-channel (e.g., multi-carrier) architectures to be exploited
to realize improvements in the transmission structure, for
instance, to improve the MC-GPRS transmission structure. An
embodiment is depicted in FIG. 3 showing an RLC/MAC block 301 being
mapped onto one radio block 303 and then onto four timeslots
305-311 belonging to four parallel TDMA frames in four parallel
carriers. A mobile terminal is able to receive the radio block 303
by monitoring all four carriers as it awaits the transmission of
the RLC/MAC block.
[0039] In an EDGE system, every radio block is sent on a different
frequency (frequency hopping system), but terminals in conventional
EDGE implementations are required to monitor only one frequency at
any given point in time.
[0040] In accordance with the invention, radio blocks may be
wirelessly transmitted via a multi-carrier transmission system to
the reduced transmission time, since a radio block may be
transmitted in a single duration, e.g., a single timeslot group of
closely spaced or contiguous timeslots. Accordingly, the
transmission time for a given amount of data using embodiments of
the invention is considerably faster than that of the conventional
GPRS transmission structure depicted in FIG. 2A. Comparing the
embodiment shown in FIG. 3 with that depicted in FIG. 2A, a radio
block in the multi-carrier system may be transmitted in parallel
over several carriers as illustrated in FIG. 3. In contrast, the
conventional system spreads the radio block over the duration of
three TDMA frames (actually, three TDMA frames plus one timeslot,
or 25 timeslots) as illustrated in FIG. 2A. Further, using
embodiments of the invention the peak transmission rate may be
quadrupled in the multi-carrier system since four carriers are used
in parallel in this example, as opposed to the use of a single
carrier in the GPRS transmission structure of FIG. 2A.
[0041] The implementation of multi-carrier transmission for radio
blocks is transparent with respect to the upper layers in as much
as embodiments of the invention do not impact SNDCP (sub network
dependent convergence protocol), LLC (logical link control) and the
RLC (radio link control) transmission parameters (e.g., window,
etc.). However, the MAC (medium access control) may be affected by
the embodiments using multi-carrier transmission. The timeslot and
timing structure of the GSM air interface does not need to be
modified. Hence, the multi-carrier redundancy improvement
embodiments may be easier to introduce than a simple multi-carrier
option where four RLC/MAC streams are sent in parallel on four
parallel carriers, with each of these streams still being
transmitted in GSM according to a GPRS protocol, for example, GPRS
R99. Using four parallel RLC/MAC streams per GPRS R99 introduces
more complications to the RLC protocol, as the four streams could
result in unpredictable behaviors for the window size and the
sequence number space at the receiver side.
[0042] Incremental redundancy schemes according to at least some
embodiments may be implemented by transmitting different redundancy
versions of the same information block. By combining the different
versions, the receiver may improve the probability of error
recovery for correct reception. The various redundancy versions may
differ in the modulation, coding or puncturing scheme. However,
redundancy versions and the primary transmission, or primary
version, are typically chosen from the same family of coding
schemes. By way of explanation, MCS coding schemes are categorized
within families (e.g., Family A (MCS-3, MCS-6 and MCS-9); Family B
(MCS-2, MCS-5 and MCS-7); and Family C (MCS-1 and MCS-4)). The
primary version and the redundancy versions should belong to the
same MCS "family." For example, if the primary transmission is
coded as MCS-7, a Family B coding scheme, the redundancy versions
should also belong to Family B; e.g., MCS-2 or MCS-5.
[0043] FIG. 4 depicts a multi-carrier system implementing a
redundancy scheme according to at least some embodiments of the
invention. As shown in the figure, a multi-carrier architecture
allows a different technique to be employed for the transmission of
the different redundancy versions on each of the carriers. This
enables various redundancy versions to be sent simultaneously using
different carriers; e.g., different frequencies. Alternatively, in
some embodiments, the various redundancy versions may be sent at
nearly the same time, but not necessarily simultaneously. For
example, the various redundancy versions may be sent within the
same transmission time period (i.e., at any time after the
transmission of the primary version begins up until the start of
the next primary version). In some implementations (e.g., some
embodiments in a GSM system), a transmission time period may be
equal to the time duration of a frame.
[0044] The data block 401 is encoded in three different redundancy
versions, 403, 405 and 407. As shown in FIG. 4, each of the three
different redundancy versions 403-407 is transmitted on its own
respective carrier 409-413 in parallel, that is, at approximately
the same time. Although each of versions 409-413 is labeled in the
figure as a "redundancy version," logically one of them may be
considered the "primary version" with the other two being
considered redundancy versions of the primary version. Other
embodiments may encode any number of different redundancy versions
to be sent simultaneously or at least within the same transmission
time period, e.g., two redundancy versions, three, four, etc.
[0045] Errors in wireless transmission due to fading tend to
correlate to particular frequencies for a given set of
circumstances. Fading over wireless links tends to be
frequency-selective, so different transmissions sent on different
carriers will likely experience different amounts of attenuation.
Use of embodiments to simultaneously send multiple redundancy
versions over different carriers provides for frequency diversity
in the multi-carrier system of FIG. 4, instead of merely providing
time diversity, as per the conventional system of FIG. 2B. In some
situations, errors may be more likely to occur in a particular
frequency range due to fading. In accordance with alternative
embodiments of the invention, if the primary version is being sent
at a frequency known to be prone to fading, a redundancy version
sent at a frequency not prone to fading may be encoded with the
same coding scheme as the primary version (e.g., primary version
subject to fading=MCS-6 and redundancy version not subject to
fading=MCS-6 also). This embodiment runs contrary to the general
rule-of-thumb of encoding the redundancy versions using differing
coding schemes from the same family. Since the coding of different
redundancy versions is the same, this embodiment is considered to
merely provide redundancy rather than incremental redundancy.
[0046] A multi-carrier incremental redundancy scheme according to
the invention may be implemented in any of several embodiments
tailored to suit the particular needs of an operator, or even
tailored to suit a given situation. For example, using self
decodable redundancy versions enable various embodiments to be
implemented using either selection combining, soft combining, or
selective soft combining Selection combining is the process of
having the receiver use only the one redundancy version that has
been selected for use. Soft combining is the process of combining
all the transmitted/received redundancy versions, using a
statistical algorithm or other means, for use in error recovery.
Selective soft combining is when some redundancy versions are
combined while others are discarded. The choice of which redundancy
version(s) to use may be implemented according to prearranged
decision making rules. One such rule is to select the first
redundancy version for combining (if an error was initially
detected) and then error check the transmitted information. The
first redundancy version (i.e., the first version to be decoded)
could for example be sent on an anchor carrier, the anchor carrier
being the main carrier of a multi-carrier structure. If an error is
still detected, then the first two redundancy versions are combined
with the primary version, and another round of error checking is
completed. Further redundancy versions are added as needed (and as
available), so long as errors continue to be detected. A receiver
may be configured with the logic to implement one or more of
selection combining, soft combining or selective soft combining,
depending upon the circumstances and parameters affecting the
transmission/reception; e.g., carrier-to-interference ratio (C/I),
air interface characteristics, noise conditions, atmospheric or
other interference conditions, jamming, allowable transmission
power, or other like circumstances and parameters affecting the
signal reception (or transmission at the other end). The decision
may be based on the measured C/I or other parameters affecting a
particular one or more of the carriers. The decision of whether to
use selection combining, soft combining or selective soft combining
may be affected solely by an algorithm, a measurement or logic
within the receiver. Alternatively, the decision may be controlled
at the transmitter end and communicated to the receiver, or may be
controlled at any intermediate point; e.g., BSC/BTS, SGSN/MSC,
within the PSTN, or other intermediate point between the two ends
of the overall communication link.
[0047] FIG. 5 depicts incremental redundancy according to at least
one embodiment of the invention in EDGE with variable
time-frequency spreading. In conventional implementations of the
EDGE system, a retransmission of the same information block due to
an error takes a different time duration for the actual
transmission itself than that of the original transmission whenever
a different MCS coding scheme is chosen for the retransmission. For
example, the transmission time of the first transmission 211 at
(MCS-6) (shown in FIG. 2B) is shorter in duration than that of the
sum of the first and second retransmissions 213 and 215 (at MCS-3),
which contain the same amount of information encoded with a
different encoding scheme. Embodiments of the present invention may
overcome this disadvantage. Accordingly, after a first transmission
performed with one MCS-6 radio block 501, the retransmission with
two MCS-3 radio blocks may be performed within a time duration no
greater in length than the first transmission.
[0048] As shown in FIG. 5, embodiments of the present invention may
exploit a multi-carrier architecture by sending the redundancy
versions via two MCS-3 retransmissions, first retransmission part
503 and second retransmission part 505, using two separate
carriers, carrier n+2 and carrier n+1, respectively. Rather than
taking a longer time duration for the actual transmission of the
redundancy versions, embodiments of the present invention use
multiple carriers to send 503 and 505 in parallel. The mapping of
MCS to number/location of carriers may either be prearranged or
determined by an algorithm, or may be specified in a look-up
table.
[0049] As is evident from FIG. 5, the two retransmitted blocks 503
and 505 may be transmitted and received in parallel. For
implementations in which it is not known at the terminal whether
the transmission will take place over one carrier, or two or more
carriers, the mobile terminal preferably monitors the parallel
carriers continuously. For example, a mobile terminal may monitor
the two or more carriers on which the retransmission will be sent
in addition to monitoring the original carrier. Having the mobile
terminal monitor the parallel carriers continuously allows
embodiments of the invention to avoid the need for an out-of-band
control channel (as is required in HSDPA or 1.times.EV-DV)
indicating when transmissions and retransmissions are to take
place. However, in alternative embodiments of the invention, an
out-of-band control channel may be used to provide carrier mapping
for the redundancy versions, or the mapping could be encoded as
part of a first sent redundancy version (or portion thereof) for
all subsequent redundancy transmissions.
[0050] FIG. 6 depicts a multi-carrier, multi-redundancy embodiment,
which provides redundancy for error recovery purposes. In the
example shown, the primary version 601 containing information
encoded using MCS-6 is sent in parallel with two other MCS-3
transmissions 603 and 605 containing the same information which
serve as the redundancy version for the primary version 601. Other
encoding schemes besides MCS-3 and MCS-6 may be used, as is known
to those of ordinary skill in the art. The embodiment depicted in
the figure may be used to provide incremental redundancy for EDGE
or for other like wireless services or systems. Such embodiments
are configured to exploit the multi-carrier architecture by
transmitting different redundancy versions simultaneously and in
parallel over different carriers. In EDGE systems, backward
compatibility is achieved by maintaining the same RLC/MAC
architecture as is used in GSM, that is, blocks belonging to the
same "family" are sent in parallel. In this embodiment, the various
redundancy versions may be transmitted via a different number of
carriers in a multi-carrier wireless system. For example, as
discussed above, the same amount of information in the form of
different redundancy versions may be sent with one MCS-9 radio
block, two MCS-6 radio blocks, and four MCS-3 radio blocks--thus
entailing the use of one, two, and four parallel carriers,
respectively. MCS-9, MCS-6 and MCS-3 are from the same family and
have a 1-2-4 code rate relationship. Alternatively, redundancy
versions may be encoded from different MCS families, so long as bit
stuffing is used to offset the differing block size of separate MCS
families.
[0051] A receiver according to embodiments of the invention may
perform any of selection combining, soft combining, or hard and
soft combining. For example, the case where the same information is
sent with MCS-6 and MCS-3 entails the transmission of three
parallel radio blocks over three carriers: one for MCS-6 and two
for the two MCS-3 radio blocks. Here, twice as many MCS-3 radio
blocks are needed since the code rate is halved. A receiver may
exploit this multi-carrier architecture as long as it receives a
subset of the transmitted blocks, for example, if any two blocks
out of the transmitted three are received.
[0052] Embodiments of the present invention allow for reduced
latency, increased peak rate, and improved coverage. Since the
receiver may perform combining of the blocks sent in parallel over
the multiple carriers, the same performance may be achieved with a
lower C/I since the instantaneous code rate is smaller. In general,
to fully exploit the capability of EDGE high values of C/I are
needed.
[0053] FIG. 7 depicts a method of setting up the initial parameters
for practicing at least one embodiment of the invention. The method
begins at 701, and proceeds to 703 for the selection of a
modulation and coding scheme for the primary version of the
information and redundancy versions. For example, a message to be
transmitted using the EDGE air interface may use 8PSK modulation
and be encoded in the MSC-6 coding scheme. In this example, the
corresponding redundancy versions could then be MCS-3 encoded using
GMSK modulation. However, the invention is not limited to these
examples and other combinations of encoding schemes known by those
of ordinary skill in the art may be used with the invention.
Further, the modulation and coding scheme do not necessarily need
to be selected each time a message is transmitted. Instead, a
default modulation and coding scheme may be used, or a predefined
modulation and coding scheme for a given set of circumstances. For
instances in which the coding scheme is being selected, either as a
default scheme or for a particular communication, it is appropriate
to tailor the encoding scheme selection to the prevailing
conditions. For example, if the reception conditions are very good,
a minimal impact redundancy scheme may be selected (i.e., the
redundancy scheme which takes up the least resources may be
determined to be appropriate). On the other hand, if reception
conditions are poor and error rates are running at relatively high
levels, a more robust redundancy scheme may be selected, which is
likely to use relatively more resources as a tradeoff for providing
better error recovery capabilities. For example, one incremental
redundancy plan which provides very robust results is to encode the
primary version of the information as one MCS-9 transmission, and
have the first redundancy version consist of two MCS-6
transmissions and a second redundancy version consisting of four
MCS-3 transmissions. Two separate redundancy versions encoded in
different formats, in addition to the initial message (primary
version), provide very good error recovery capabilities.
[0054] Once the coding scheme has been selected in block 703, the
method proceeds to 705 where a transmission strategy is determined.
The term transmission strategy is used herein to include the
relative timing for sending the various
transmissions/retransmissions. For example, the primary version of
the information could be sent first (e.g, 501 of FIG. 5), and one
or more redundancy versions simultaneously sent at a later time
(e.g., 503 and 505 of FIG. 5). In at least one embodiment, a second
redundancy version is sent. This may be done at the same time the
first redundancy version is sent (e.g., same time period as 503 and
505), or may be performed at a later time. Alternatively, all
versions (e.g., the primary version and all redundancy versions)
may be sent at the same time (e.g., FIG. 4 or FIG. 6). In at least
one embodiment of the invention the transmission strategy may be
predetermined so that the receiver knows when and where to monitor
a second carrier, or simultaneously monitor two or more carriers,
in order to receive the redundancy versions. Having the
transmission strategy prearranged avoids the need for out-of-band
signaling as is required in conventional systems.
[0055] The selection of a coding scheme in block 703 and
prearranging transmission strategy in block 705 may affect each
other, and may be performed either in tandem or in any order. For
example, it may be possible to select a transmission strategy (705)
before choosing a coding scheme (703). These activities may be
performed during an initial step-up stage or provisioning period
and set as a default condition. The choice of a coding scheme and
transmission strategy may be later altered, as needed, to better
adapt to current conditions; e.g., reception conditions,
communication traffic patterns and schedules, revenue
considerations, as well as various other like types of conditions
such as the timing and quality considerations dependent upon
various types of content. For instance, the transmission of voice
needs real-time error recovery (or very small delays for error
recovery) versus content in which minor delays may be acceptable
such as Internet browsing or email applications.
[0056] Once the coding schemes and transmission strategies have
been selected, the method proceeds to 707 for the selection of any
other communication protocols, as are known by those of ordinary
skill in the art. Such protocols may include the parameters used in
provisioning various network equipment (e.g., SGSN 102, BSC/BTS 104
and/or mobile units 120 of FIG. 1A), or parameters needed to set up
or tear down communications links. Once the communication protocols
have been selected in block 707, the method proceeds to 709 where
it is completed. In 709 the various parameters, which were selected
in 701 through 707, may be stored for future use, and communicated
to those portions of the system where needed. The parameters may be
stored in memory 108 of the SGSN 102 shown in FIG. 1A, or elsewhere
within the system.
[0057] FIG. 8 depicts a method for practicing at least one
embodiment of the invention to provide error recovery for wireless
communication systems. In block 801, the initial parameters are set
up as explained above in conjunction with FIG. 7. Once the initial
parameters have been set up, the method proceeds to 803 where it is
determined whether there is information to be transmitted. If there
is no information to be transmitted, the method proceeds according
to the "NO" branch from 803 to block 805 to wait for a message, and
then loops back to 803 to again determine whether there is a
message to be transmitted. In block 803, if it is determined that
there is information to be transmitted, the method proceeds
according to the "YES" branch from 803 to 807 to encode the
information to be transmitted. In some embodiments, even if it has
been determined that there is information to be transmitted and the
method has proceeded to block 807 or further for processing the
information, the system also continues to monitor for additional
messages to be transmitted in accordance with block 805. That is,
some steps for processing messages to be transmitted may be handled
in parallel as the system continues to monitor for new messages to
be transmitted in block 805. In block 807, the message is encoded
according to the protocols previously defined in the initialization
phase, as depicted in FIG. 7.
[0058] In one exemplary embodiment, the primary version of the
message may be encoded using one MCS-9 transmission. Once the
primary version of the message has been encoded, the method
proceeds to 809 to encode one or more redundancy versions. For
example, given the exemplary embodiment using one MCS-9 block for
the primary version of the information, a first redundancy version
may consist of two MCS-6 transmissions along with a second
redundancy version of four MCS-3 transmissions. It should be noted
that most embodiments described herein involve actions taken to
handle the redundancy versions (blocks 809-815) in response to the
primary version being obtained and encoded, not in response to
receiving any sort of out-of-band signal to send a redundancy
version. A redundancy version is considered to be transmitted in
response to the transmission of the primary version when, as a
result of obtaining the information to send in block 803 the system
encodes one or more redundancy versions for transmission. This is
evident, for example, from FIG. 4 in which all versions are sent
simultaneously. In embodiments in which the redundancy versions are
not sent simultaneously with the primary version, but are sent
within the same transmission time period (i.e., at a time after the
primary version transmission begins up until the start of the next
primary version) the redundancy versions are sent in response to
transmission of the primary version. In some implementations (e.g.,
some embodiments in a GSM system), a transmission time period will
be equal to the time duration of a frame. Once the redundancy
versions have been encoded the method proceeds to block 811.
[0059] In block 811 the carriers may be selected in accordance with
the communication scheme being used, or to conform to the protocols
or specifications of the system. Once the carriers for the primary
version and the one or more redundancy versions have been selected,
the method proceeds to 813 where the various versions are
transmitted, either simultaneously or in some staggered manner, for
example, as per the exemplary embodiments discussed in conjunction
with FIGS. 3-6. As discussed above, the transmission of the
redundancy versions may be performed in response to the primary
version being transmitted, not in response to receiving any sort of
out-of-band signal with information of a data failure or
instructions to send a redundancy version. The transmission of the
primary version and redundancy version(s) typically takes place
from a stationary base station (e.g., BSC/BTS 104 of FIG. 1A) to a
mobile unit (e.g., 120). Hence, blocks 801-813 typically take place
in a stationary BTS or SGSN, while block 815 (and the blocks of
FIG. 9) typically occur in a mobile unit. However, in some
embodiments the mobile unit may transmit a primary version and one
or more redundancy versions. The message transmissions taking place
in block 813 may be a single transmission (e.g., SMS message) or
may be one of a number of transmissions (e.g., a bit of speech
being transmitted as part of an on-going telephone conversation).
For each primary transmission and the associated redundancy
versions, the transmission of block 813 may be followed by block
815 for decoding the various transmissions, and combining them if
an error is detected. The various embodiments may use any of
selection combining, soft combining, and/or selective soft
combining, depending upon the scheme being implemented and
prevailing reception conditions. Once the transmissions have been
decoded and combined to produce a combined version of the received
transmissions, the method proceeds to block 817. In an alternative
embodiment, block 817 is performed only once (or not at all) before
the communication link is torn down. In some embodiments or in
certain situations block 817 is not performed, and instead the
method proceeds directly from block 815 to 805.
[0060] In 817, it is determined whether conditions exist to warrant
changes or updates to the redundancy scheme, or aspect of it. For
example, if a redundancy scheme is in place which calls for only
one redundancy version and the error rate is still at an
unacceptably high level, the conditions may warrant changing the
redundancy scheme to transmit two or more redundancy versions
associated with the primary version. Another example of an
alteration to the redundancy scheme may come in the form of
changing the method of combining the redundancy versions. For
example, if the redundancy scheme in place uses selection
combining, but the error rate is higher than a predetermined
threshold, then the scheme may be changed to soft combining or
selective soft combining, in an effort to provide better error
recovery if the prevailing air interface conditions are preventing
error recovery. Block 817 may involve changing carriers to avoid
interference and/or transmission errors due to fading, which may be
correlated to particular frequencies in a given set of conditions.
Since different transmissions sent on different carriers may be
subject to varying amounts of attenuation, a change in carrier
frequency may improve the error recovery results. Further, block
817 may include any changes made due to new versions of software,
downloaded patches, updates to incorporate modifications to telecom
specifications, or other like types of periodic maintenance to the
system. Upon completion of 817 and once any changes or updates to
the redundancy scheme have been implemented, the method proceeds
back to 805 to wait for the next message to be transmitted.
[0061] FIG. 9 depicts a block diagram for a method of decoding and
combining redundancy versions according to at least one embodiment.
Typically these activities take place in a mobile unit or other
receiver in which embodiments of the invention are implemented. The
blocks depicted in FIG. 9 provide some detail about decoding,
combining and error recovery that may take place in the block 815
of the previous figure. The method begins in block 901 where an
error check is performed to determine whether the primary version
of the transmitted information contains errors. The error check may
involve any sort of routine or algorithm specified by the system,
the system operator, or conducted within the mobile unit itself.
For example, the error detection may involve a redundancy check
such as checksum, a cyclical redundancy check (CRC), a frame check
sequence (FCS), or error correction codes (ECC) such as Hamming
codes, Reed-Solomon code, Reed-Muller code, Binary Golay code,
convolutional code, turbo code, or other like type of error
detection or detection/correction scheme. These, or other like
routines known to those of ordinary skill in the art, may be used
in an error recovery scheme. Different types of actions may be
taken in block 901 to ascertain whether there are errors such as
making a channel measurement or received power measurement, a
positive or a negative ACK, an implicit estimate of mobile unit
reception quality, or any other like type of routine or test for
errors in reception known to those of ordinary skill in the art.
Alternatively, if the reception conditions are known to be below a
predetermined level, a received transmission may be assumed to
contain errors for the purpose of utilizing the redundancy versions
transmitted in accordance with embodiments of the invention until
such time as reception conditions are known to improve. Upon
completion of error detection in block 901, the method proceeds to
the decision block 903. If no error is detected in the
transmission, the method proceeds from block 903 to block 905 in
accordance with the "NO" branch to wait for another transmission
and then loops back to block 901. In some embodiments, a default
condition may be specified in which one or more of the redundancy
versions are combined with the primary version (the "YES" branch)
regardless of whether or not errors have been detected. In the
event an error is detected, the method proceeds from block 903 to
block 907 in accordance with the "YES" branch for determination of
whether selection combining is to be performed.
[0062] The method of error recovery may be predetermined to default
to selection combining, selective soft combining, soft combining,
or a combination of these error recovery routines. Alternatively,
the type of error recovery may be varied or otherwise selected to
best suit the conditions, depending upon the reception conditions,
prevailing traffic conditions, economics or other like parameters
for selecting a type of error recovery. In any event, at block 907
if selection combining is to be used the method proceeds in
accordance with the "YES" branch to block 909 where a redundancy
version of the message is selected for use in error recovery. If,
at block 907, it is determined that selection combining is not to
be used for error recovery, the method proceeds from 907 to 911
where it is determined whether selective soft combining is to be
used. If, at block 911, it is determined that selective soft
combining is to be used for error recovery the method proceeds from
911 to 913 via the "YES" branch for the selection and soft
combining of one or more redundancy versions so that selective soft
combining error recovery may be performed. If selective soft
combining is not to be used, the method proceeds from block 911 to
block 915 in accordance with the "NO" branch. If it is determined
that selection combining (907) and selective soft combining (911)
are not to be used, in accordance with block 915 the available
redundancy versions may be soft combined for use in error
recovery.
[0063] Once one of the error recovery techniques have been chosen
(e.g., selection combining, selective soft combining, soft
combining, or other like error recovery technique), the method
proceeds to block 917 and the selected redundancy version, or the
soft-combination of the selected redundancy versions, are decoded.
Once the aforementioned process is completed the method proceeds to
919 for an error recovery routine. Block 919 may entail similar
activities to those performed in error checking the primary version
in block 901 (or block 815 of the previous figure). In some
embodiments, if the error recovery of block 919 fails, the method
loops back to 901 for further processing of the data. This is
depicted as a dotted line between 919 and 901. For example, in a
first pass selection combining may have been chosen (or
prearranged) in accordance with block 907. On a second pass, in
block 907 a second redundancy version could be combined with the
primary version and the first redundancy version, or alternately,
soft combining (915) or selective combining (911) may be selected
on the second or subsequent passes.
[0064] The figures are provided to explain and enable the invention
and to illustrate the principles of the invention. Some of the
activities for practicing the invention shown in the method block
diagrams of the figures may be performed in an order other than
that shown in the figures. For example, in FIG. 8 the selection of
the carriers (811) may take place before encoding the redundancy
versions (809). Further, those of ordinary skill in the art
understand that information and signals may be represented using
any of a variety of different technologies and techniques. For
example, data, instructions, commands, information, signals, bits,
symbols, and chips that may be referenced throughout the above
description may be represented by voltages, currents,
electromagnetic waves, magnetic fields or particles, optical fields
or particles, or any combination thereof.
[0065] Those of ordinary skilled in the art will also appreciate
that the various illustrative logical blocks, modules, circuits,
and algorithm routines described in connection with the embodiments
disclosed herein may be implemented as electronic hardware,
computer software, firmware, or combinations thereof. To clearly
illustrate this interchangeability of hardware and software,
various illustrative components, blocks, modules, circuits, and
steps have been described above generally in terms of their
functionality. Whether such functionality is implemented as
hardware or software depends upon the particular application and
design constraints imposed on the overall system. Practitioners of
ordinary skill in the art will know to implement the described
functionality in varying ways for each particular application, but
such implementation decisions should not be interpreted as causing
a departure from the scope of the present invention.
[0066] The various illustrative logical blocks, modules, and
circuits described in connection with the embodiments disclosed
herein may be implemented or performed with a general purpose
processor, a digital signal processor (DSP), an application
specific integrated circuit (ASIC), a field programmable gate array
(FPGA) or other programmable logic device, discrete gate or
transistor logic, discrete hardware components, or any combination
thereof designed to perform the functions described herein. A
general purpose processor may be a microprocessor, but in the
alternative, the processor may be any conventional processor,
controller, microcontroller, computer or state machine. A processor
may also be implemented as a combination of computing devices,
e.g., a combination of a DSP and a microprocessor, a plurality of
microprocessors, one or more microprocessors in conjunction with a
DSP core, or any other such configuration.
[0067] The activities of methods, routines or algorithms described
in connection with the embodiments disclosed herein may be embodied
directly in hardware, in a software module executed by a processor,
or in a combination of the two. A software module may reside in RAM
memory, flash memory, ROM memory, EPROM memory, EEPROM memory,
registers, hard disk, a removable disk, a CD-ROM, or any other form
of storage medium known in the art. An exemplary storage medium is
coupled to the processor in such a manner that the processor may
read information from, and write information to, the storage
medium. In the alternative, the storage medium may be integral to
the processor. The processor and the storage medium may reside in
an ASIC. The ASIC may reside in a user terminal. In the
alternative, the processor and the storage medium may reside as
discrete components in a user terminal.
[0068] Various modifications to the illustrated and discussed
embodiments will be readily apparent to those of ordinary skill in
the art, and the principles defined herein may be applied to other
embodiments without departing from the spirit or scope of the
invention. Thus, the present invention is not intended to be
limited to the embodiments shown herein but is to be accorded the
widest scope consistent with the principles and novel features
disclosed herein.
[0069] In describing various embodiments of the invention, specific
terminology has been used for the purpose of illustration and the
sake of clarity. However, the invention is not intended to be
limited to the specific terminology so selected. It is intended
that each specific term includes equivalents known to those of
skill in the art as well as all technical equivalents which operate
in a similar manner to accomplish a similar purpose. Hence, the
description is not intended to limit the invention. The invention
is intended to be protected broadly within the scope of the
appended claims.
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